Spider silks are nature's high-performance polymers, obtaining extraordinary toughness due to a combination of strength and elasticity. Spiders have up to seven different glands which produce a variety of silk types with different mechanical properties and functions. Dragline silk, produced by the major ampullate gland, is the toughest fiber, and on a weight basis it outperforms man-made materials, such as tensile steel. The properties of dragline silk are attractive in development of new materials for medical or technical purposes.
Dragline silk consists of two main polypeptides, mostly referred to as major ampullate spidroin (MaSp) 1 and 2, but e.g. as ADF-3 and ADF-4 in Araneus diadematus. These proteins have molecular masses in the range of 200-720 kDa. The genes coding for dragline proteins of Latrodectus hesperus are the only ones that have been completely characterized, and the MaSp1 and MaSp2 genes encode 3129 and 3779 amino acids, respectively (Ayoub N A et al. PLoS ONE 2(6): e514, 2007). The properties of dragline silk polypeptides are discussed in Huemmerich, D. et al. Curr. Biol. 14, 2070-2074 (2004).
Spider dragline silk proteins, or MaSps, have a tripartite composition; a non-repetitive N-terminal domain, a central repetitive region comprised of many iterated poly-Ala/Gly segments, and a non-repetitive C-terminal domain. It is generally believed that the repetitive region forms intermolecular contacts in the silk fibers, while the precise functions of the terminal domains are less clear. It is also believed that in association with fiber formation, the repetitive region undergoes a structural conversion from random coil and α-helical conformation to β-sheet structure. The C-terminal region of spidroins is generally conserved between spider species and silk types. The N-terminal domain of spider silks is the most conserved region (Rising, A. et al. Biomacromolecules 7, 3120-3124 (2006)).
WO03/057727 discloses expression of soluble recombinant silk polypeptides in mammalian cell lines and animals. The obtained silk polypeptides exhibit poor solubility in aqueous media and/or form precipitates. Since the obtained silk polypeptides do not polymerise spontaneously, spinning is required to obtain polymers or fibers.
WO07/078239 and Stark, M. et al. Biomacromolecules 8, 1695-1701, (2007) disclose a miniature spider silk protein consisting of a repetitive fragment with a high content of Ala and Gly and a C-terminal fragment of a protein, as well as soluble fusion proteins comprising the spider silk protein. Fibers of the spider silk protein are obtained spontaneously upon liberation of the spider silk protein from its fusion partner. The small fusion unit is sufficient and necessary for the fiber formation.
Hedhammar, M. et al. Biochemistry 47, 3407-3417, (2008) study the thermal, pH and salt effects on the structure and aggregation and/or polymerisation of recombinant N- and C-terminal spidroin domains and a repetitive spidroin domain containing four poly-Ala and Gly rich co-blocks.
In vitro studies on the biocompatibility of recombinant spider silk are so far few, and the materials studied vary a lot in amino acid sequence, mode of production and format.